The present invention relates to an optical device connected to an optical fiber transmission line, capable of receiving or transmitting/receiving a light signal, and a method for producing the same.
Wavelength division multiplexing (WDM) enables a transmission capacity of an optical transmission system to be increased. It also realizes bidirectional transmission and simultaneous transmission of different kinds of signals. Thus, the WDM is capable of flexibly meeting service requirements in an optical transmission system, and is applicable to various optical transmission systems such as a relay-transmission system, a subscriber system, and a local area transmission system.
In recent years, in particular, optical subscriber systems which transmit multi-channel video information and data from a central station to households through optical fibers have been proposed and studied. These systems require a plurality of photodetectors for simultaneously receiving different kinds of light signals which are multiplexed in wavelength at subscribers"" household terminals and light-emitting devices for sending requests and data from households to the central station. For example, a device used for this purpose is disclosed in a reference (I. Ikushima et al., xe2x80x9cHigh-performance compact optical WDM transceiver module for passive double star subscriber systemsxe2x80x9d, Journal of Lightwave Technology, vol. 13, No. Mar. 3, 1995).
FIG. 30 shows a conventional example of a light-receiving optical device which is applicable to bidirectional signal transmission. This device is disclosed in Japanese Laid-Open Patent Publication No. 6-331837.
As shown in FIG. 30, in this device, a first optical fiber 2012 and a second optical fiber 2014 are coupled in series with a gap (about several xcexcm) therebetween. One end of the first optical fiber 2012 is cut obliquely with respect to an optical axis and provided with a semi-transparent and semi-reflective surface 2011 which reflects a part of a light signal and passes the remaining part. Similarly, one end of the second optical fiber 2014 is cut obliquely with respect to an optical axis and provided with a semi-transparent and semi-reflective surface 2013 which reflects a part of a light signal and passes the remaining part.
The first and second optical fibers 2012 and 2014 are arranged in such a manner that the semi-transparent and semi-reflective surface 2013 of the second optical fiber faces the semi-transparent and semi-reflective surface 2011 of the first optical fiber 2012 and the respective optical axes are linearly aligned.
A light signal propagating from the right side of the drawing is reflected by the semi-transparent and semi-reflective surface 2011 of the first optical fiber 2012 and output from the optical fiber 2012. A first photodiode 2015 is placed along a path of the light signal and receives the light signal to generate an electric signal.
A light signal propagating from the left side of the drawing is reflected by the semi-transparent and semi-reflective surface 2013 of the second optical fiber 2014 and output from the optical fiber 2014. A second photodiode 2016 is placed along a path of the light signal and receives the light signal to generate an electric signal.
In the conventional optical device, a semi-transparent and semi-reflective surface is directly formed on the diagonally-cut facet of each optical fiber. Because of this, (1) a special cutting is required to be conducted with respect to the facet of an optical fiber so as to make it smooth or grinding the facet of an optical fiber after diagonally cutting it is required. Furthermore, (2) in order to form a semi-transparent and semi-reflective surface on the facet of an optical fiber, it is required to form a thin film on the facet of the optical fiber. The step of inserting an optical fiber into a thin film deposition apparatus such as a vacuum deposition apparatus and depositing a thin film on the facet of the optical fiber decreases production through-put.
In addition, the ends of two different optical fibers are separately cut diagonally with respect to optical axes, and then, arranged in such a manner that the respective optical axes are aligned. Therefore, (3) it is required to adjust the optical axes with high precision; and (4) the light propagation loss between two optical fibers is likely to increase due to the shift of the optical axes and the transmission loss is varied depending upon devices. Furthermore, (5) there is a difference in refractive index between the optical fibers and the air under the condition that the optical axes of two optical fibers are aligned, even with an optical fiber gap of about several xcexcm. Therefore, signal light is refracted in the gap, and the transmission loss is likely to greatly increase.
The present invention has been achieved in view of the above-mentioned problems, and its objective is to provide a compact, integrated, and light-weight optical device with improved productivity at low cost.
Another objective of the present invention is to provide a bidirectional optical device connected to an optical fiber transmission line, receiving and transmitting a light signal, and a method for producing the same.
An optical device of the present invention includes: a substrate; at least one first groove formed on the substrate; an optical fiber provided in the first groove; and at least one second groove diagonally traversing the optical fiber. The device further includes an optical member which is inserted in the second groove and has a surface reflecting or diffracting at least a part of light propagating through the optical fiber.
In a preferred embodiment, a material having a refractive index nr which is almost equal to a refractive index nf of a core portion of the optical fiber is embedded at least between the optical member and the optical fiber in the second groove.
In a preferred embodiment, there is a relationship: 0.9xe2x89xa6(nr/nf)xe2x89xa61.1 between the refractive index nr and the refractive index nf.
In a preferred embodiment, the material having the refractive index nr is made of resin.
In a preferred embodiment, the material having the refractive index nr is made of UV-curable resin.
In an embodiment, minute unevenness is present on an inner wall of the second groove.
In an embodiment, the optical member selectively reflects light having a wavelength in a selected range.
In an embodiment, the optical member selectively passes light having a wavelength in a selected range.
In a preferred embodiment, the optical member includes a base made of a material having a refractive index nb and a dielectric multi-layer film formed on the base, and there is a relationship: 0.9xe2x89xa6(nb/nf)xe2x89xa61.1 between the refractive index nb and the refractive index nf.
In an embodiment, the surface of the optical member has a diffraction grating.
In an embodiment, the substrate is made of a material which is transparent to signal light propagating through the optical fiber.
In an embodiment, the substrate is made of glass.
In an embodiment, the substrate is made of ceramic.
In an embodiment, the substrate is made of a semiconductor.
In a preferred embodiment, a normal to the surface of the optical member is not parallel to an optical axis of the optical fiber.
In a preferred embodiment, the second groove is tilted with respect to an upper surface of the substrate.
In an embodiment, at least one optical element which receives light reflected or diffracted by the optical member is provided on the substrate.
In an embodiment, at least one second optical element which receives light passed through the optical member is further provided on the substrate.
In an embodiment, the substrate has an upper surface and a bottom surface, and the device further includes: a first photodetector which is provided on the bottom surface of the substrate and receives light reflected or diffracted by the optical member; and a second photodetector which is provided on the upper surface of the substrate and receives light reflected or diffracted by the optical member.
In an embodiment, the substrate has an upper surface and a bottom surface on which a reflector is attached, and the device further includes: a first photodetector which is provided on the upper surface of the substrate and receives light reflected or diffracted by the optical member; and a second photodetector which is provided on the upper surface of the substrate and receives light reflected or diffracted by the optical member via the reflector.
The above-mentioned substrate has an upper surface, a bottom surface, and a plurality of side surfaces, and the device further includes: a first photodetector which is provided on one of the plurality of side surfaces of the substrate and receives light reflected or diffracted by the optical member; and a second photodetector which is provided on another side surface of the plurality of side surfaces of the substrate and receives light reflected or diffracted by the optical member.
In an embodiment, the optical element is a photodetector which generates an electric signal in accordance with received light.
In a preferred embodiment, the photodetector is fixed onto the substrate.
In a preferred embodiment, a material having a refractive index np which is almost equal to a refractive index nf of a core portion of the optical fiber is embedded between a light-receiving surface of the photodetector and the substrate.
In an embodiment, a low reflectance film is formed on the light-receiving surface of the photodetector.
In an embodiment, the number of the second groove is plural, and optical members having different filter characteristics are inserted in the plurality of second grooves, respectively.
In an embodiment, the number of the first groove is plural, the number of the second groove is singular, and the single second groove traverses the plurality of first grooves.
In an embodiment, the number of the first groove is plural, and the plurality of first grooves are arranged on the substrate almost in parallel with each other.
In an embodiment, a third groove is formed on the substrate in a direction crossing the first groove, another optical fiber is provided in the third groove, and light reflected or diffracted by the optical member is coupled to the another optical fiber.
In an embodiment, laser light emitted by a semiconductor laser is coupled to an end portion of the optical fiber.
In an embodiment, the substrate has a concave portion on the upper surface, a semiconductor laser is provided on the concave portion of the substrate, the end portion of the optical fiber is formed in a lens shape, and light emitted by the semiconductor laser is optically coupled to the optical fiber.
In an embodiment, the end portion of the optical fiber has a movable portion capable of moving a position of the lens-shaped portion relative to the semiconductor laser device, and the movable portion is fixed in such a manner that light emitted by the semiconductor laser is optically coupled to the optical fiber.
In an embodiment, the substrate has a concave portion on the upper surface, and the device includes a semiconductor laser provided on the concave portion of the substrate and a lens which optically couples light emitted by the semiconductor laser to the optical fiber.
In an embodiment, a support member supporting the semiconductor laser and the lens is provided on the concave portion of the substrate.
In a preferred embodiment, the semiconductor laser provided on the support member is provided on the concave portion of the substrate after being selected by a test.
In an embodiment, a photodetector which receives a part of laser light from the semiconductor laser is provided on the substrate.
In an embodiment, the optical fiber has a first portion which functions as a single mode fiber in a wavelength band of signal light propagating through the optical fiber, a second portion which functions as a multi-mode fiber in the wavelength band of the signal light, and a connecting portion connecting the first portion to the second portion, and a core diameter of the connecting portion gradually and continuously changes from the first portion to the second portion.
In an embodiment, a core diameter of the second portion which functions as the multi-mode fiber of the optical fiber is increased by heat-treating a part of a single mode fiber.
In an embodiment, the another optical fiber in the third groove is made of a multi-mode fiber, and a photodetector which receives light reflected or diffracted by the optical member through the another optical fiber is further provided.
In an embodiment, an electric wiring pattern is formed on the substrate, and the photodetector is connected to the electric wiring pattern.
In an embodiment, a semiconductor electric element which conducts a signal processing of the photodetector is connected to the electric wiring pattern.
In an embodiment, one end of the optical fiber is provided with an optical connector so as to be connected to another optical fiber.
In an embodiment, a protecting film formed so as to cover an upper surface of the substrate is further provided.
In an embodiment, the substrate is accommodated in a housing having an output port of the optical fiber and a plurality of terminals electrically connected to outside.
In an embodiment, the semiconductor laser is connected to the support member with a first solder material, and the support member is connected to the substrate with a second solder material having a melting point higher than a melting point of the first solder material.
In an embodiment, the substrate is accommodated in a housing having an output port of the optical fiber and a plurality of terminals electrically connected to outside, and the substrate is connected to a bottom portion of the housing with a third solder material having a melting point lower than a melting point of the second solder material.
Another optical device of the present invention includes: a substrate, at least one first groove formed on the substrate; an optical fiber provided in the first groove, which allows signal light to propagate bidirectionally; and at least one second groove diagonally traversing the optical fiber. The device further includes: an optical member inserted in the second groove, having a surface which reflects or diffracts at least a part of the bidirectional signal light propagating through the optical fiber; and two photodetectors respectively receiving light reflected or diffracted by the optical member of the bidirectional signal light.
In an embodiment, the above-mentioned device further includes a third groove which traverses the optical fiber and a second optical member inserted in the third groove, having a surface which reflects and removes light containing an unnecessary wavelength component propagating through the optical fiber.
In an embodiment, the second groove is perpendicular to an optical axis of the optical fiber.
In an embodiment, the second groove and the third groove are formed at different angles with respect to an optical axis of the optical fiber so that light reflected by the second optical member inserted in the third groove is not mixed in the two photodetectors.
In a preferred embodiment, a material having a refractive index nr which is almost equal to a refractive index nf of a core portion of the optical fiber is embedded at least between the optical member and the optical fiber in the second groove.
In a preferred embodiment, there is a relationship: 0.9xe2x89xa6(nr/nf)xe2x89xa61.1 between the refractive index nr and the refractive index nf.
In an embodiment, the material having the refractive index nr is made of resin.
In an embodiment, the material having the refractive index nr is made of UV-curable resin.
In an embodiment, minute unevenness is present on an inner wall of the second groove.
In an embodiment, the optical member selectively reflects light having a wavelength in a selected range.
In an embodiment, the optical member selectively passes light having a wavelength in a selected range.
In an embodiment, the optical member includes a base made of a material having a refractive index nb and a dielectric multi-layer film formed on the base, and there is a relationship: 0.9xe2x89xa6(nb/nf)xe2x89xa61.1 between the refractive index nb and the refractive index nf.
In an embodiment, the surface of the optical member has a diffraction grating.
In an embodiment, the substrate is made of a material which is transparent to signal light propagating through the optical fiber.
In an embodiment, the substrate is made of a glass material.
In an embodiment, the substrate is made of a plastic material.
In an embodiment, the bidirectional signal light has wavelengths different from each other, the optical member has a base which is transparent and has a refractive index almost equal to a refractive index of the optical fiber and two reflective coatings formed on two principal planes of the base, and the two reflective coatings exhibit different reflection characteristics, respectively.
In an embodiment, the reflective coating is made of a metal thin film.
In an embodiment, the two reflective coatings respectively have a multi-layer thin film structure.
In an embodiment, each of the two photodetectors is provided in a can-shaped housing by sealing, and two concave portions are formed on the substrate so as to engage with the can-shaped housings.
In an embodiment, the two photodetectors are connected to an electric wiring pattern formed on the substrate.
In an embodiment, the electric wiring pattern is connected to an electric integrated circuit element which detects an electric signal output from at least one of the two photodetectors and processes the electric signal.
In an embodiment, the optical fiber has a first portion which functions as a single mode fiber in a wavelength band of signal light propagating through the optical fiber, a second portion which functions as a multi-mode fiber in the wavelength band of the signal light, and a connecting portion connecting the first portion to the second portion, and a core diameter of the connecting portion gradually and continuously changes from the first portion to the second portion.
In an embodiment, the substrate is accommodated in a housing having an output port of the optical fiber and a plurality of terminals electrically connected to outside.
In an embodiment, a wavelength of light propagating bidirectionally through the optical fiber is in a 1.3 xcexcm band and/or a 1.5 xcexcm band, and a wavelength of unnecessary light which is removed by the second optical member is in a 0.98 pm band or a 1.48 pm band.
A method for producing an optical device of the present invention includes the steps of: forming a first groove on an upper surface of a substrate; embedding and fixing a part of an optical fiber in the first groove; forming a second groove so as to diagonally traverse the optical fiber; and inserting and fixing an optical member having a surface which reflects or diffracts at least a part of light propagating through the optical fiber in the second groove.
In a preferred embodiment, the step of inserting and fixing the optical member in the second groove includes the step of embedding a material having a refractive index nr almost equal to a refractive index nf of a core portion of the optical fiber at least between the optical member and the optical fiber in the second groove.
In a preferred embodiment, there is a relationship: 0.9xe2x89xa6(nr/nf)xe2x89xa61.1 between the refractive index nr and the refractive index nf.
In an embodiment, the above-mentioned method further includes the step of providing at least one photodetector on the substrate.
In an embodiment, the above-mentioned method further comprising the step of providing at least one photodetector on the substrate.
In an embodiment, the above-mentioned method further includes the step of providing at least one laser diode on the substrate.
Another method for producing an optical device of the present invention includes the steps of: forming a plurality of first grooves on an upper surface of a substrate; embedding and fixing a part of optical fibers in each of the plurality of first grooves; forming a second groove so as to diagonally traverse the plurality of optical fibers; and inserting and fixing an optical member having a surface which reflects or diffracts at least a part of light propagating through the optical fibers in the second groove.
In a preferred embodiment, an angle formed by a direction of a normal to the surface of the optical member and a direction of an optical axis of the optical fiber is in the range of 5xc2x0 to 40xc2x0.
An optical device of the present invention includes: a substrate; at least one first groove formed on the substrate; an optical fiber provided in the first groove; and a facet of the surface which diagonally traverses the optical fiber. The device further includes: an optical member attached to the facet of the substrate with a material having a refractive index almost equal to a refractive index of a core portion of the optical fiber, having a surface which reflects or diffracts at least a part of light propagating through the optical fiber; and a photodetector provided on the substrate, receiving light reflected by the optical member of the part of the light propagating through the optical fiber.
In an embodiment, the photodetector is provided on a surface of the substrate on which the first groove is formed.
In an embodiment, the photodetector is provided on a surface opposite to the surface of the substrate on which the first groove is formed.
In an embodiment, the above-mentioned device includes: a third groove which traverses the optical fiber; and a second optical member inserted in the third groove, which reflects light in a specified wavelength region, wherein the second optical member prevents the light in the specified wavelength region propagating through the optical fiber from being incident upon the photodetector.
In an embodiment, the above-mentioned device includes an optical member attached to an upper surface of the substrate with a resin material having a refractive index almost equal to a refractive index of a core portion of the optical fiber, which reflects light in a specified wavelength region, wherein the photodetector is provided on the optical member.
In an embodiment, a filter having a dielectric multi-layer film structure is formed on a light-receiving surface of the photodetector.
In an embodiment, the optical fiber is connected to an optical fiber light transmission line.
In an embodiment, the optical fiber is provided with a ferrule portion so as to be connected to an optical fiber transmission line.
Another method for producing an optical device of the present invention includes the steps of: forming a first groove on a substrate; fixing an optical fiber in the first groove; diagonally cutting the optical fiber to form a facet tilted with respect to an optical axis of the optical fiber on the substrate; attaching an optical member having a surface which reflects or diffracts at least a part of light propagating through the optical fiber to the tilted facet with a material having a refractive index almost equal to a refractive index of a core portion of the optical fiber; and providing a photodetector which receives light reflected or diffracted by the optical member on the substrate.
As described above, in the optical device of the present invention, an optical fiber is embedded in a groove of a substrate, and an optical member which reflects or diffracts light propagating through the optical fiber is embedded in the substrate, whereby signal light can be taken out in any direction.
Furthermore, the light taken out in any direction is coupled to a semiconductor photodetector placed above the substrate without forming any unnecessary reflected point, by using resin whose refractive index is matched with that of the optical fiber. In particular, when a multi-mode optical fiber is used, the coupling is made easier.
The filter characteristics of the optical member are improved by embedding both sides of an element using a layer having a multi-layer film structure composed of a dielectric and metal with a resin material having a refractive index almost equal to that of the optical fiber, or by embedding only a plane different from a principal plane of a certain kind of optical member with a resin material having a refractive index almost equal to that of the optical fiber.
Light to be taken out by diffraction is coupled to a semiconductor photodetector array or taken outside using another optical fiber, whereby only light with a desired wavelength can be easily separated from light signals having a plurality of different wavelengths.
In the case where the optical fiber is a multi-mode optical fiber connected to a single mode fiber, with a core diameter of a connecting portion thereof gradually and continuously changing, or in the case where the optical fiber is a multi-mode fiber obtained by heat-treating the single mode fiber and the optical fiber, light can be coupled to the single mode fiber at high efficiency by coupling light to the multi-mode fiber with a mode diameter increased.
When a semiconductor laser is placed on a concave portion of a substrate and an optical fiber having a lens function is used, light can be easily coupled to the optical fiber. When a movable portion is provided at a part of the embedded optical fiber, the semiconductor laser is connected to the substrate, and then, the movable portion of the optical fiber is adjusted, whereby the coupling degree of light to the optical fiber can be increased.
When a semiconductor laser and a lens are provided on different substrates, and an optical fiber is provided on an embedding substrate, the semiconductor laser can be used after its characteristics are tested, so that the yield of the optical device can be improved. Light of the semiconductor laser can be coupled to the optical fiber with low precision of about several xcexcm by prescribing an imaging spot of light of the semiconductor laser formed by the lens to be almost equal to that of the multi-mode fiber.
When light is taken out from a substrate through a multi-mode fiber, all the light is taken in a semiconductor light-receiving apparatus, whereby an analog signal can be received without any degradation of quality.
An electric wiring pattern for connection to semiconductor light-receiving and light-emitting devices can be formed on the surface of a substrate, and particularly in the case of a high frequency signal, the impedance can be matched to that of an electric circuit connected to outside. Furthermore, when an electric element which processes an electric signal is integrally formed in addition to the semiconductor light-receiving and light-emitting devices, an electric matching becomes satisfactory and the optical device can be miniaturized.
When different reflective elements are arranged so as to separately receive signals with different wavelengths from an optical fiber embedded in a substrate, a light signal transmitted with wavelengths being multiplexed can be selectively taken out of one substrate.
When a plurality of optical fibers are arranged in an array on a substrate, light signals are independently transmitted in parallel through a plurality of optical fibers in one substrate.
After devices are formed on a substrate, the surface of the substrate is covered with a resin material, whereby a semiconductor device provided on the surface of the substrate can be protected from water, an atmosphere, etc. from outside. The substrate can be accommodated as it is in a housing having an optical fiber output port and electric connection terminals.
Furthermore, the melting point of a first solder material between a semiconductor laser and a substrate is prescribed to be higher than that of a second solder material between the substrate and another substrate, and the melting point of the second solder material is prescribed to be higher than that of a third solder material connecting the substrate to the housing. Thus, devices are prevented from moving during the respective connections using the solder material, whereby reliability can be secured.